General properties of polymers: pick the correct statement about conductivity, crystallinity, vaporisation, and changes with increasing degree of polymerisation.

Introduction / Context:
Polymer properties evolve with molecular weight and microstructure. Recognising qualitative trends is essential for processing and application choices in plastics, rubbers, and fibres.

Given Data / Assumptions:

• Most common polymers are thermal and electrical insulators.
• Polymers may be amorphous, semicrystalline, or (rarely) highly crystalline.
• On extreme heating, polymers typically degrade thermally rather than vaporise cleanly.

Concept / Approach:
Increasing the degree of polymerisation (DP) raises molecular weight, viscosity, softening point, and mechanical strength. A typical qualitative sequence for the same chemistry is liquid → greasy/oily → waxy → rubbery/solid as chain length grows. Conductivity is generally low for organic polymers. Crystallinity depends on tacticity, branching, and chain regularity; many important polymers are only semicrystalline. Thermal decomposition precedes true vaporisation for most polymers due to covalent backbone scission.

Step-by-Step Solution:
Evaluate (a): False — polymers are usually poor conductors.Evaluate (b): False — many are amorphous or semicrystalline.Evaluate (c): False — decomposition occurs before clean vaporisation.Evaluate (d): True — describes the qualitative change with increasing DP.

Verification / Alternative check:
Polymer synthesis texts describe viscosity and softening increases with molecular weight; processing windows reflect this behaviour.

Why Other Options Are Wrong:
(a) and (b) contradict broad polymer behaviour; (c) ignores thermal degradation.

Common Pitfalls:
Confusing crystallinity with orientation; drawing may increase orientation without drastically changing crystallinity in some cases.

Final Answer:
A liquid polymer becomes greasy, then waxy, and finally solid as the degree of polymerisation increases.